Where, in a machine, it is necessary to join two portions thereof in order to prevent the pasage through said joints of a fluid or gaseous medium, the mode of sealing will depend on whether the two parts of the machine move in relationship to each other or are static in relationship to each other once the machine is assembled. Where the machine parts move relative to each other, for example, in an automobile piston moving in an automobile cylinder, the sealing problem is designated as dynamic sealing. On the other hand, where, in a similar machine, the cylinder head is connected to connected to the cylinder block, the two parts do not move relative to each other and the sealing is designated as static sealing. It is with this latter form of sealing that the present invention is concerned. In most, although not all, modes of static sealing, there are utilized gasket means which are substantially annular in plan view and have a predetermined generally, but not exlusively, circular cross section. A prime example of this type of gasket means is the "O" ring. Such gasket means are employed in the sealing of flanges, lids, stoppers, screws, and the like.
For static sealing, one may also employ substantially flat gasket means as, for example, the gasket means employed between the head and the block of an automobile cylinder. While these means are available for the provision of sealing against higher pressures, they employ substantially harder and less elastic sealing materials, and require a high initial stressing force which necessarily leads to greater expenses.
On the other hand, where O-rings are used, in so far as they are sufficiently elastic, only minimal initial stressing forces are required, and they automatically form themselves into a sealing pattern. The advantage of the O-ring type of sealing means is that as the pressure in the contained volume rises, the gaseous or fluid medium pressing on the exposed surface of the O-ring automatically transfers the pressure onto the working faces of the mutually abutting surfaces of the equipment. Since the sealing rings have, because of their nature, a radial or axial initial stress, the sealing force will always exceed the force exerted by the gaseous or liquid medium.
The O-rings utilized heretofore have usually been made of rubber or other elastomers of varying qualities and hardnesses which have, unfortunately, the common disadvantage that they have a relatively short working life. This working life is shortened by higher temperatures, particularly in the presence of air, which "age" the rubber or elastomer partly through oxidation and partly through further vulcanization. These two factors increase the hardness of the gasket means and, at the same time, reduce the elasticity and flexibility thereof leading, ultimately, to rupture. Elastomeric O-rings must, therefore, be periodically replaced. Where the sealing of dangerous media is concerned, for safety reasons, the replacement must be carried out at intervals which are so short that no problems of ageing in the gasket means can be allowed to have appeared.
Furthermore, there are certain circumstances under which the utilization of elastomeric gasket means is not permissable. These circumstances include, for example, very low temperatures -- that is to say, below minus 60.degree. C. -- or very high temperatures -- that is to say, above about 200.degree. C. -- in the presence of chemically active substances which attack the elastomeric material or, more recently, radioactive media.
It would therefore be desirable to provide a gasket sealing means for static sealing in strip or suitably ring form, the elasticity of which does not deteriorate through ageing, which is utilizable up to 500.degree. C., and which is substantially unaffected by even strong radioactive radiation.